To meet customer demand, the ability to detect and identify image quality defects such as weak or missing jets during a print run is critical for some printers. Missing jets produce thin sharp streaks which are visible. Such streaks are objectionable to a customer. Countermeasures can be applied in the print engine to correct or mitigate the effects of missing jets. In order to apply these countermeasures, it is often necessary to reliably know the location and color separation identity of the missing jets. Missing jets can appear at any time, so it is necessary to look for them rather frequently. It is relatively straight-forward to detect and identify image quality (IQ) defects such as weak or missing jets (WMJ) with the use of test patterns. However, it is undesirable to insert test patterns into a customer's job. Not only does this waste paper and reduce productivity, but these pages need to be removed from the job. This adds cost and complexity to a print job and provides opportunities for mistakes to occur. Consequently it is desirable to be able to detect such defects using scanned images of actual customer prints rather than test patterns.
Methods have arisen which attempt to identify, at a pixel-level, the color of each halftone dot and then analyze the dots for defects. For approaches that do not identify individual halftone dots directly, the resolution can be lower but they require some form of mapping that relates the average sensor outputs to the average colorant inputs for all possible levels. Such derived mapping using a RGB sensor for a CMYK printer is non-unique. Additional information, such as GCR level used, is often needed. For approaches that attempt to identify individual halftone dots directly, there is no need to derive or apply the above mapping. However, these require higher sensing resolution so that the halftone dots can be properly resolved (generally 2-times to 4-times higher resolution depending on the sensor MTF). A suitable sensor for this category would be a 1200DPI×1200DPI or even a 2400DPI×2400DPI RGB FWA. This may not be viable for all printing systems.
Accordingly, what is needed in this art are increasingly sophisticated systems and methods which overcome the challenges of insufficient sensor resolution in high speed printing systems such that halftone dots present on a customer's print can be analyzed for image quality defect detection.
Incorporated References
The following U.S. patents, U.S. patent applications, and Publications are incorporated herein in their entirety by reference.
“Systems And Methods For Monitoring Jets With Full Width Array Linear Sensors”, U.S. Pat. No. 7,810,896, to Mizes et al.
“Identification Of Faulty Jets Via Sensing On Customer Images”, U.S. Publication No. 20100303281, by Wu et al.
“Banding Defect Detection In Digital Imaging Systems”, U.S. patent application Ser. No. 12/552,519, by Xu et al.
“Identification Of Faulty Jets Via Sensing On Customer Images”, U.S. patent application Ser. No. 12/474,711 by Wu et al.
“System And Method For Detecting Missing Ink Jets In An Inkjet Printer Using Image Data Of Printed Documents Without Apriori Knowledge Of The Documents”, U.S. application Ser. No. 12/906,694, by Wu et al.
“Color Calibration For Digital Halftoning”, U.S. Pat. No. 6,435,654, to Wang et al.